Autoreactive CD4+ T cells are present at low frequency in peripheral blood, often with low antigen avidity, and show reactivity to multiple autoantigens. Nevertheless, they are central determinants of autoimmunity, guiding not only specificity and magnitude of immune responses, but also critically involved in the balance between disease progression and regulation. We propose to exploit recent advances in several areas[unreadable] multimer technology, T1D prediction, cellular microarrays, and humanized mouse models[unreadable]in order to develop profiles for islet antigen-reactive T cells associated with T1D susceptibility, disease, and protection. In Aim 1, HLA class II tetramers (for six islet antigens) and class I tetramers (for two islet antigens) will be used together with flow cytometry techniques to compare T cell characteristics among well-characterized human subjects at risk for T1D or with progressive disease;In Aim 2, we will analyze the functional properties of one of the important phenotypes associated with T1D[unreadable]namely, the low avidity autoreactive CD4+ T cells. A partially humanized mouse model created for this purpose will enable a detailed evaluation of the activation and homing properties. In Aim 3, new technologies designed to translate research techniques into more sensitive and rapid clinical tests will be developed, in order to advance T cell profiling into a more useful clinical research tool. These studies will be closely integrated with other elements of the Autoimmunity Cooperative Group, both at UCHSC and at other sites, and the resources derived in this project will be disseminated to the other sites, as well.